A gathering write operation writes, in a single invocation, a
sequence of bytes from one or more of a given sequence of buffers.
Gathering writes are often useful when implementing network protocols or
file formats that, for example, group data into segments consisting of one
or more fixed-length headers followed by a variable-length body. Similar
scattering read operations are defined in the ScatteringByteChannel interface.

Suppose that a byte sequence of length n is written, where
0<=n<=r.
Up to the first srcs[offset].remaining() bytes of this sequence
are written from buffer srcs[offset], up to the next
srcs[offset+1].remaining() bytes are written from buffer
srcs[offset+1], and so forth, until the entire byte sequence is
written. As many bytes as possible are written from each buffer, hence
the final position of each updated buffer, except the last updated
buffer, is guaranteed to be equal to that buffer's limit.

Unless otherwise specified, a write operation will return only after
writing all of the r requested bytes. Some types of channels,
depending upon their state, may write only some of the bytes or possibly
none at all. A socket channel in non-blocking mode, for example, cannot
write any more bytes than are free in the socket's output buffer.

This method may be invoked at any time. If another thread has
already initiated a write operation upon this channel, however, then an
invocation of this method will block until the first operation is
complete.

Parameters:

srcs - The buffers from which bytes are to be retrieved

offset - The offset within the buffer array of the first buffer from
which bytes are to be retrieved; must be non-negative and no
larger than srcs.length

length - The maximum number of buffers to be accessed; must be
non-negative and no larger than
srcs.length - offset